Charlie was an older guy that I first worked when I was just an apprentice instrument tech. Here is Charlie's law for lab instrument repair.

"Knowledge is in knowing that tapping it with a Hammer will fix it. True skill in knowing where to tap it and how hard to tap"

Another adage from our shop(from our chief instrument tech)

"Anyone can fix it with parts, it takes real talent to make it work without any"

Needless to say the work quality from our shop improved markedly when those two retired.